Programmed cell death 4 (PDCD4) enhances the sensitivity of gastric cancer cells to TRAIL-induced apoptosis by inhibiting the PI3K/Akt signaling pathway

The molecular targets of Kangai injection in gastric cancer by in silico network pharmacology approach and experiment confirmation

INTRODUCTION

This study aimed to identify the phytochemical constituents that could target gastric cancer in Kangai injection using a network pharmacology-based approach.

METHODS

Protein-protein interactions (PPI), Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were conducted utilizing String and OmicShare tools. In the in vitro experiments, the related mRNA and protein levels were assessed via real-time quantitative polymerase chain reaction and Western blotting, respectively. Cell proliferation was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay.

RESULTS

Kangai injection comprises several compounds, which target multiple substrates and pathways related to gastric cancer. The PPI and Gene Ontology analyses revealed that tumor necrosis factor (TNF) was a hub gene. KEGG pathway enrichment analysis indicated that the the TNF pathway was significantly enriched. Kangai injection decreased the mRNA levels of TNFR2, TRAF2, PI3K, AKT, and IκBα and inhibited the phosphorylation of PI3K, AKT, and IκBα phosphorylations. Kangai injection inhibited cell proliferation, while TNFR2 overexpression or treatment with the PI3K activator 740 Y-P partially restored it.

CONCLUSION

Kangai injection operates through multiple targets and pathways in gastric cancer, with the TNFR2/PI3K/AKT/NF-κB pathway playing a crucial role in its mechanism against gastric cancer.

Celastrus orbiculatus Extract Reduces Stemness of Gastric Cancer Stem Cells by Targeting PDCD4 and EIF3H

BACKGROUND

Celastrus orbiculatus ethyl acetate extract (COE) has shown a strong anti-gastric cancer effect, but the understanding of its mechanism is still lacking. The results of previous studies indicated that COE may be able to inhibit the stemness of gastric cancer stem cells (GCSCs) by regulating PDCD4 and EIF3H expression.

AIMS

To explore if COE could inhibit the stemness of GCSCs by regulating PDCD4 and EIF3H expression in vitro and in vivo.

PROCEDURE

The GCSCs model was established by stem cell-conditioned culture. Spheroid formation and flow cytometry assays were used to detect the effect of COE on the spheroid formation ability of GCSCs and the percentage of CD44⁺/CD24⁺ and ALDH⁺ cell subpopulations. Western blot analysis was applied to measure the expression of GCSCs biomarkers (Nanog, Oct-4, and SOX-2), PDCD4, and EIF3H in GCSCs treated with COE; and RT-PCR was performed to investigate the effect of COE on PDCD4 mRNA expression in GCSCs. An in vivo tumorigenicity experiment was also conducted to evaluate the effect of COE on tumor-initiating ability of GCSCs in vivo; and the expression of PDCD4 and EIF3H in xenograft tissues was examined by immunohistochemistry (IHC) staining.

RESULTS

After culture in stem cell-conditioned medium, SGC7901 cells manifested significantly enhanced spheroid formation ability, upregulated Nanog, Oct-4, and SOX-2 expression and increased percentages of CD44⁺/CD24⁺ and ALDH⁺ cell subpopulations, indicating successful establishment of the GCSCs model. COE treatment significantly inhibited the spheroid formation ability of GCSCs and reduced the percentage of CD44⁺/CD24⁺ and ALDH⁺ cell subpopulations. The western blot analysis showed a significant decrease of Nanog, Oct-4, SOX-2, and EIF3H expression and an increase of PDCD4 expression in GCSCs after COE treatment in a concentration-dependent manner. COE treatment also significantly upregulated the mRNA expression of PDCD4 in GCSCs. In addition, COE displayed a strong inhibitory effect on the tumor-initiating ability of GCSCs in vivo and upregulated PDCD4 and downregulated EIF3H expression in xenograft tissues.

CONCLUSION

COE may be able to inhibit GC growth by suppressing the stemness of GCSCs via regulating PDCD4 and EIF3H expression.

miR-21 sustains CD28 signalling and low-affinity T-cell responses at the expense of self-tolerance

Objective

miR-21 is highly expressed in iNKT and activated T cells, but its T-cell autonomous functions are poorly defined. We sought to investigate the role of miR-21 in the development and functions of T and iNKT cells, representing adaptive and innate-like populations, respectively.

Methods

We studied mice with a conditional deletion of miR-21 in all mature T lymphocytes.

Results

Thymic and peripheral T and iNKT compartments were normal in miR-21 KO mice. Upon activation in vitro, miR-21 depletion reduced T-cell survival, T_H17 polarisation and, remarkably, T- and iNKT cell ability to respond to low-affinity antigens, without altering their response to high-affinity ones. Mechanistically, miR-21 sustained CD28-dependent costimulation pathways required to lower the T-cell activation threshold, inhibiting its repressors in a positive feedback circuit, in turn increasing T-cell sensitivity to antigenic stimulation and survival. Upon immunisation with the low-affinity self-epitope MOG_35-55, miR-21 KO mice were indeed less susceptible than WT animals to the induction of experimental autoimmune encephalomyelitis, whereas they mounted normal T-cell responses against high-affinity viral epitopes generated upon lymphocytic choriomeningitis virus infection.

Conclusion

The induction of T-cell responses to weak antigens (signal 1) depends on CD28 costimulation (signal 2). miR-21 sustains CD28 costimulation, decreasing the T-cell activation threshold and increasing their sensitivity to antigenic stimulation and survival, broadening the immune surveillance range. This occurs at the cost of unleashing autoimmunity, resulting from the recognition of weak self-antigens by autoreactive immune responses. Thus, miR-21 fine-tunes T-cell response and self-/non-self-discrimination.

Rafoxanide promotes apoptosis and autophagy of gastric cancer cells by suppressing PI3K /Akt/mTOR pathway

Rafoxanide is commonly used as anti-helminthic medicine in veterinary medicine, a main compound of salicylanilide. Previous studies have reported that rafoxanide, as an inhibitor of BRAF V600E mutant protein, inhibits the growth of colorectal cancer, multiple myeloma, and skin cancer. However, its therapeutic effect on gastric cancer (GC) and the potential mechanism has not been investigated. Here, we have found that rafoxanide inhibited the proliferation of GC cells in vitro, arrested the cell cycle in the G0/G1 phase, and promoted apoptosis and autophagy in GC cells. Treatment with specific autophagy inhibitor 3-methyladenine drastically inhibited the apoptotic cell death effect by suppressing the switch from autophagy to apoptosis. Mechanistically, we found that rafoxanide inhibited the growth of GC cells in vitro by inhibiting the activity of the PI3K/Akt/mTOR signaling pathway. This process induced autophagy, which essentially resulted in the apoptosis of GC cells. Results from subcutaneous implanted tumor models in nude mice also indicated that rafoxanide inhibited the growth of GC cells in vivo. Taken together, our findings revealed that rafoxanide inhibited the growth of GC cells both in vitro and vivo, indicating a potential drug candidate for the treatment of GC.

Clinical significance of decreased programmed cell death 4 expression in patients with giant cell tumors of the bone

Programmed cell death 4 (PDCD4) has been recognized as a novel tumor suppressor gene, which inhibits the activation and translation of activator protein (AP)-1. Dysregulated expression of PDCD4 is also involved in various human tumors and is linked to tumor progression and development. However, the function and clinical implication of PDCD4 in giant cell tumors of the bone (GCTBs) has not been previously investigated. In the present study, PDCD4 expression was determined in 83 samples of GCTBs at mRNA and protein levels by quantitative reverse transcription-polymerase chain reaction, western blotting and immunohistochemistry. The results demonstrated that PDCD4 mRNA expression was reduced in 63% of GCTB samples (17/27) and protein expression was decreased in 65% of samples (54/83), compared with adjacent non-tumor tissues. Furthermore, decreased expression of PDCD4 was significantly associated with certain clinicopathological characteristics, including the Campanacci grade and recurrence. A strong negative correlation was determined between PDCD4 expression and the Ki-67 positive rate in GCTBs (r=−0.6392; P<0.001). The results of the present study suggest that PDCD4 may serve a role in the malignant progression of human GCTBs and may be an important prediction factor for prognosis.

MiR-1260b inhibitor enhances the chemosensitivity of colorectal cancer cells to fluorouracil by targeting PDCD4/IGF1

Colorectal cancer (CRC) is the most common malignant tumor type and has become resistant to 5-fluorouracil (5-FU) in recent decades, which is one of the most popular therapies. Recently, microRNA (miRNA or miR) has been investigated as a potential therapeutic strategy for CRC. However, there has been little investigation of the underlying mechanism of the association between expression of miRNA and chemosensitivity. The present study aimed to investigate the effect of miR-1260b inhibitor on CRC cells, and their chemosensitivity to 5-FU, by treating them with the miR-1260b inhibitor. miR-1260b inhibitor was demonstrated to significantly promote the proliferation and invasion of the CRC cell line, HCT116, and to increase the apoptotic rate. Furthermore, it was validated that programmed cell death 4 (PDCD4) was a direct target of miR-1260b inhibitor in CRC with bioinformatics tools and a luciferase assay. Western blot analysis revealed that miR-1260b inhibitor could significantly decrease PDCD4 expression, and downregulate the expression of phosphorylated-Akt (p-Akt) and phosphorylated-extracellular-signal-regulated kinase (p-ERK). In conclusion, it was confirmed that the anti-tumor effect of the miR-1260b inhibitor was conducted by blocking the phosphorylated 3-kinase/Akt pathway as dysregulated protein expression induced by miR-1260b inhibitor was rescued by insulin-like growth factor. Notably, miR-1260b inhibitor could significantly enhanced the chemoresponse of HCT116 cells to 5-FU via reduced proliferation, increased apoptosis, and downregulation of PDCD4, p-Akt and p-ERK protein expression. In summary, the present study may provide a novel direction for future clinical therapy to enhance the chemosensitivity of tumor cells.

Combined application of Embelin and tumor necrosis factor-related apoptosis-inducing ligand inhibits proliferation and invasion in osteosarcoma cells via caspase-induced apoptosis

Embelin, as an inhibitor of the X-linked inhibitor of apoptosis protein (XIAP), may induce apoptosis in various types of cancer cells. The present study aimed to determine the effect of Embelin on the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of osteosarcoma cells. Embelin and TRAIL were applied to U2OS and MG63 cells, respectively or in combination. MTT was initially used to detect the difference in survival rates between the group receiving combined application of 100 ng/ml TRAIL and 20 µmol/l Embelin and the individual application groups. Light microscopic quantification was used to detect the morphology of the osteosarcoma cells in each group. Determination of cell apoptosis was subsequently performed using flow cytometry. The invasive ability of the cells was detected by a Transwell assay, prior to relative protein expression being determined by western blot analysis. Based on all the test data, it was revealed that the survival rates and the invasive ability were significantly lower following the combined application of 100 ng/ml TRAIL and 20 µmol/l Embelin than following the individual application of either (P<0.01). Additionally, upregulating expression of caspases, as well as death receptor 5, and downregulating expression of XIAP and matrix metalloproteinase 9 (MMP-9), had more significant effects in the combined group compared with the individual group and the control group. All these results suggested that Embelin may enhance TRAIL-induced apoptosis and inhibit the invasion of human osteosarcoma cells.

Defining the regulatory role of programmed cell death 4 in laryngeal squamous cell carcinoma

Programmed cell death 4 (PDCD4) is decreased in many different kinds of malignant tumors. EMT endows tumor cells invasive and metastatic properties. However, few studies have determined the role of PDCD4 in the regulation of EMT in the context of laryngeal carcinoma. We examined the relationship between PDCD4 and EMT-associated proteins E-cadherin and N-cadherin using laryngeal carcinoma tissues. Gene manipulation was used to define the regulatory capacity of PDCD4. We report that PDCD4 and E-cadherin/N-cadherin expression were significantly changed in the carcinoma tissues, and their expression was associated with pathological grade, metastatic state, and clinical stage. The suppression of PDCD4 (and consequently, E-cadherin) was concomitant with increased proliferation and G2-phase arrest, decreased apoptosis, and increased cell invasion. PDCD4 upregulation reversed the above-mentioned results. In nude mice, PDCD4 knockdown increased tumor growth and pathological features, confirming the tumorigenic role of PDCD4. Finally, PDCD4 silencing was associated with dysregulation of the carcinogenic Wnt-β-catenin and the STAT3-miR-21 signaling pathways. This study revealed a dynamic regulatory relationship between PDCD4 and critical factors for EMT, establishing a broad, functional role for PDCD4 in laryngeal carcinoma, which may be propagated by the STAT3-miR-21 pathway. These findings provide new information on an EMT-associated target that may lead to a novel therapy.

Thioridazine upregulates programmed cell death 4 to induce apoptosis in nasopharyngeal carcinoma through the PI3K/Akt signalling pathway

Thioridazine (THZ) has been identified as a potential regulator of tumour progression, and programmed cell death 4 (PDCD4) has been reported as a novel tumour suppressor. This study aimed to investigate the link between PDCD4 and THZ in the regulation of nasopharyngeal cancer (NPC) cell proliferation. The effect of THZ on NPC cells was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays. Then, the involvement of apoptosis and cell cycle in the THZ-mediated regulation of cell viability was assessed by flow cytometry. Related mRNAs and proteins were subsequently examined by real-time PCR and western blot, respectively. After transfection with the PDCD4-siRNA, pGC-FU-GFP-PDCD4 vector and phosphoinositide 3-kinase (PI3K) inhibitor Ly294002, we investigated the antagonistic effects of THZ and PDCD4 on NPC-related protein expression. MTT assays showed that THZ treatment suppressed cell viability. THZ-treated cells were arrested at the G1/G0 phase and showed a significantly increased apoptotic fraction. Furthermore, PDCD4-siRNA antagonized THZ treatment and promoted NPC cell proliferation. Western blot analysis showed that PDCD4 overexpression or PI3K inhibition by LY294002 significantly reduced the expression of phospho-PI3K, phospho-Akt, phospho-mammalian target of rapamycin and phospho-p70s6k, but not their total protein levels. In conclusion, our findings show that THZ and PDCD4 exert antagonistic effects on NPC cell proliferation, probably through the PI3K/Akt pathway. Moreover, these results provide an insight into the mechanism by which THZ targets PDCD4 in NPC cell lines and suggest that the ectopic expression of PDCD4 is a potential therapeutic strategy.

Noncoding RNA in drug resistant sarcoma

Sarcomas are a group of malignant tumors that arise from mesenchymal origin. Despite significant development of multidisciplinary treatments for sarcoma, survival rates have reached a plateau. Chemotherapy has been extensively used for sarcoma treatment; however, the development of drug resistance is a major obstacle limiting the success of many anticancer agents. Sarcoma biology has traditionally focused on genomic and epigenomic deregulation of protein-coding genes to identify the therapeutic potential for reversing drug resistance. New and more creative approaches have found the involvement of noncoding RNAs, including microRNAs and long noncoding RNAs in drug resistant sarcoma. In this review, we discuss the current knowledge of noncoding RNAs characteristics and the regulated genes involved in drug resistant sarcoma, and focus on their therapeutic potential in the future.

miR-181b functions as an oncomiR in colorectal cancer by targeting PDCD4

Programmed cell death 4 (PDCD4) is a RNA-binding protein that acts as a tumor suppressor in many cancer types, including colorectal cancer (CRC). During CRC carcinogenesis, PDCD4 protein levels remarkably decrease, but the underlying molecular mechanism for decreased PDCD4 expression is not fully understood. In this study, we performed bioinformatics analysis to identify miRNAs that potentially target PDCD4. We demonstrated miR-181b as a direct regulator of PDCD4. We further showed that activation of IL6/STAT3 signaling pathway increased miR-181b expression and consequently resulted in downregulation of PDCD4 in CRC cells. In addition, we investigated the biological effects of PDCD4 inhibition by miR-181b both in vitro and in vivo and found that miR-181b could promote cell proliferation and migration and suppress apoptosis in CRC cells and accelerate tumor growth in xenograft mice, potentially through targeting PDCD4. Taken together, this study highlights an oncomiR role for miR-181b in regulating PDCD4 in CRC and suggests that miR-181b may be a novel molecular therapeutic target for CRC.

Endogenous molecular network reveals two mechanisms of heterogeneity within gastric cancer

Intratumor heterogeneity is a common phenomenon and impedes cancer therapy and research. Gastric cancer (GC) cells have generally been classified into two heterogeneous cellular phenotypes, the gastric and intestinal types, yet the mechanisms of maintaining two phenotypes and controlling phenotypic transition are largely unknown. A qualitative systematic framework, the endogenous molecular network hypothesis, has recently been proposed to understand cancer genesis and progression. Here, a minimal network corresponding to such framework was found for GC and was quantified via a stochastic nonlinear dynamical system. We then further extended the framework to address the important question of intratumor heterogeneity quantitatively. The working network characterized main known features of normal gastric epithelial and GC cell phenotypes. Our results demonstrated that four positive feedback loops in the network are critical for GC cell phenotypes. Moreover, two mechanisms that contribute to GC cell heterogeneity were identified: particular positive feedback loops are responsible for the maintenance of intestinal and gastric phenotypes; GC cell progression routes that were revealed by the dynamical behaviors of individual key components are heterogeneous. In this work, we constructed an endogenous molecular network of GC that can be expanded in the future and would broaden the known mechanisms of intratumor heterogeneity.

Silencing of miR-21 sensitizes CML CD34+ stem/progenitor cells to imatinib-induced apoptosis by blocking PI3K/AKT pathway

BCR-ABL tyrosine kinase inhibitor imatinib fails to eradicate leukemia stem cells (LSCs), the underlying mechanisms maintaining CML LSCs remain poorly understood. Here, we showed that transient inhibition of miR-21 by antagomiR-21 markedly increased imatinib-induced apoptosis in CML, but not normal CD34+ stem/progenitor cells. Furthermore, PI3K inhibitors also significantly sensitized CML CD34+ cells to imatinib-induced apoptosis. MiR-21 or PI3K inhibitor in combination with imatinib treatment significantly decreased AKT phosphorylation and c-Myc expression than either agent did alone, but did not affect Bim and Bcl-6 expresssion. These findings indicate that miR-21 is required for maintaining the imatinib-resistant phenotype of CML CD34+ cells through PI3K/AKT signaling pathway, thus providing the basis for a promising therapeutic approach to eliminate CML LSCs.

PDCD4 as a predictor of sensitivity to neoadjuvant chemoradiotherapy in locally advanced rectal cancer patients

OBJECTIVE

The purpose of this study was to examine the role of programmed cell death 4 (PDCD4) expression in predicting tumor response to neoadjuvant chemoradiotherapy and outcomes for patients with locally advanced rectal cancer.

METHODS

Clinicopathological factors and expression of PDCD4 were evaluated in 92 patients with LARC treated with nCRT. After the completion of therapy, 4 cases achieved clinical complete response (cCR), and thus the remaining 88 patients underwent a standardized total mesorectal excision procedure. There were 38 patients (41.3%) with a good response (TRG 3-4) and 54 (58.7%) with a poor one (TRG 0-2).

RESULTS

Immunohistochemical staining analyses showed that patients with high expression of PDCD4 were more sensitive to nCRT than those with low PDCD4 expression (P=0.02). High PDCD4 expression before nCRT and good response (TRG3-4) were significantly associated with improved 5-year disease-free survival and 5-year overall survival (P<0.05). Multivariate analysis demonstrated that the pretreatment PDCD4 expression was an independent prognostic factor.

CONCLUSION

Our study demonstrated that high expression of PDCD4 protein is a useful predictive factor for good tumor response to nCRT and good outcomes in patients with LARC.

Restoring TRAIL mediated signaling in ovarian cancer cells

Ovarian cancer has emerged as a multifaceted and genomically complex disease. Genetic/epigenetic mutations, suppression of tumor suppressors, overexpression of oncogenes, rewiring of intracellular signaling cascades and loss of apoptosis are some of the deeply studied mechanisms. In vitro and in vivo studies have highlighted different molecular mechanisms that regulate tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mediated apoptosis in ovarian cancer. In this review, we bring to limelight, expansion in understanding systematical characterization of ovarian cancer cells has led to the rapid development of new drugs and treatments to target negative regulators of TRAIL mediated signaling pathway. Wide ranging synthetic and natural agents have been shown to stimulate mRNA and protein expression of death receptors. This review is compartmentalized into programmed cell death protein 4, platelet-derived growth factor signaling and miRNA control of TRAIL mediated signaling to ovarian cancer. Mapatumumab and PRO95780 have been tested for efficacy against ovarian cancer. Use of high-throughput screening assays will aid in dissecting the heterogeneity of this disease and increasing a long-term survival which might be achieved by translating rapidly accumulating information obtained from molecular and cellular studies to clinic researches.

MicroRNA-21 regulates biological behaviors in papillary thyroid carcinoma by targeting programmed cell death 4

BACKGROUND

Our recent study has found that microRNA-21 (miRNA-21) was significantly upregulated in papillary thyroid carcinoma (PTC) tissues compared with nontumor tissues by using miRNA microarray chip. However, the function of miRNA-21 is unknown in PTC. The aim of this study was to investigate the roles of miRNA-21 in PTC and the mechanism of gene regulation by it.

METHODS

We transfected PTC cell line (TPC-1) with pEZX-eGFP-miRNA-21 plasmid to determine the biological functions of miRNA-21. Western blot assay was applied to investigate the correlation between miRNA-21 and programmed cell death 4 (PDCD4) expression in TPC-1 cell line.

RESULTS

Overexpression of miRNA-21 could significantly enhance proliferation and invasion and inhibit the apoptosis of TPC-1 cells. In addition, miRNA-21 and PDCD4 expression showed a significantly negative correlation in TPC-1 cells.

CONCLUSIONS

These data suggest that miRNA-21 may play an oncogenic role by directly targeting PDCD4 in the cellular processes of PTC. In addition, the findings in our present study also may represent new clues for the diagnostic and therapeutic strategies in the treatment of PTC.

Tumor suppressor PDCD4 modulates miR-184-mediated direct suppression of C-MYC and BCL2 blocking cell growth and survival in nasopharyngeal carcinoma

Programmed cell death 4 (PDCD4), a novel tumor suppressor, inhibits cell proliferation, migration and invasion as well as promotes cell apoptosis in tumors. However, the molecular mechanism of its tumor-suppressive function remains largely unknown in tumors including nasopharyngeal carcinoma (NPC). In this study, downregulated PDCD4 expression was significantly associated with the status of NPC progression and poor prognosis. PDCD4 markedly suppressed the ability of cell proliferation and cell survival by modulating C-MYC-controlled cell cycle and BCL-2-mediated mitochondrion apoptosis resistance signals, and oncogenic transcription factor C-JUN in NPC. Furthermore, miR-184, a tumor-suppressive miRNA modulated by PDCD4 directly targeting BCL2 and C-MYC, participated in PDCD4-mediated suppression of cell proliferation and survival in NPC. Further, we found that PDCD4 decreased the binding of C-Jun to the AP-1 element on the miR-184 promoter regions by PI3K/AKT/JNK/C-Jun pathway and stimulated miR-184 expression. In clinical fresh specimens, reduced PDCD4 mRNA level was positively correlated with miR-184 expression in NPC. Our studies are the first to demonstrate that PDCD4 as tumor suppressor regulated miR-184-mediated direct targeting of BCL2 and C-MYC via PI3K/AKT and JNK/C-Jun pathway attenuating cell proliferation and survival in NPC.

Sodium nitroprusside (SNP) sensitizes human gastric cancer cells to TRAIL-induced apoptosis

AIM

To investigate the effects of the nitrous oxide (NO)-donor sodium nitroprusside (SNP) on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in human gastric cancer cells.

METHODS

The MTT assay and flow cytometry were used to detect cellular proliferation and markers of apoptosis, respectively. Expression levels of caspases-8, and 9 were determined by Western blot. Changes in Nitric Oxide Synthase (NOS) activity, NO production, and caspase activation were also evaluated.

RESULTS

We found that TRAIL induced apoptosis and cell cycle arrest in human gastric cancer cell lines, and that this effect was mediated by NO production, and activation of both the extrinsic and intrinsic signaling pathways of apoptosis. In addition, we found that the NO-donor SNP sensitizes gastric cancer cells to TRAIL-mediated apoptosis. Treatment of cells with both TRAIL and SNP resulted in increased activation of caspase-8 and caspase-9 and NO release. Inhibition of caspase-8 blocked cell TRAIL-induced apoptosis, while a selective caspase-9 inhibitor was unable to prevent apoptosis induced by either TRAIL or TRAIL plus SNP. Inhibition of NOS could block the activation of caspase-9, but had no obvious effect on cell apoptosis.

CONCLUSIONS

SNP-sensitized gastric cancer cells to TRAIL-induced cytotoxicity by stimulating the release of NO, in turn facilitating the mitochondria-mediated signal transduction pathway. The engagement of the mitochondria signaling pathways along with the TRAIL death receptor signaling pathway synergistically increase levels of apoptosis in these cells.

Tumor suppressor gene PDCD4 negatively regulates autophagy by inhibiting the expression of autophagy-related gene ATG5

PDCD4 (programmed cell death protein 4), a suppressor of gene transcription and translation, plays a crucial inhibitory role in several types of human tumors. However, its underlying mechanisms remain unclear. Autophagy, an evolutionarily conserved catabolic process, maintains cellular homeostasis under stress conditions such as starvation and plays a crucial role in tumor initiation and progression. We report here that PDCD4 inhibits autophagy in multiple cell types both in vitro and in vivo, which in turn contributes to its tumor suppressor activity. Importantly, PDCD4 inhibits the expression of an essential autophagy related gene, ATG5 and the formation of an ATG12-ATG5 complex, and its ma3 domains are required for PDCD4-mediated inhibition of autophagy. Unlike most tumor suppressors that act as positive or dual regulators of autophagy, our findings indicate that PDCD4 negatively regulates autophagy by targeting ATG5, which provides a novel mechanism of tumor suppression.

MicroRNAs and metastasis-related gene expression in Egyptian breast cancer patients

AIM AND BACKGROUND

MicroRNAs (miRNAs) are a class of naturally occurring small noncoding RNAs that regulate gene expression, cell growth, differentiation and apoptosis by targeting mRNAs for translational repression or cleavage. The present study was conducted to study miRNAs in Egyptian breast cancer (BC) and their relation to metastasis, tumor invasion and apoptosis in addition to their association with the ER and PR statuses.

METHODS

Real Time RT-PCR was performed to identify the miRNA expression level of eight miRNAs and eight metastatic-related genes in 40 breast cancer samples and their adjacent non-neoplastic tissues. The expression levels of each miRNA relative to U6 RNA were determined. Also, miRNA expression profiles of the BC and their corresponding ANT were evaluated.

RESULTS

The BC patients showed an up-regulation in miRNAs (mir-155, mir-10, mir-21 and mir-373) with an upregulation in MMP2, MMp9 and VEGF genes. We found down regulation in mir-17p, mir-126, mir-335, mir-30b and also TIMP3, TMP1 and PDCD4 genes in the cancer tissue compared to the adjacent non-neoplastic tissues. Mir -10b, mir -21, mir-155 and mir373 and the metastatic genes MMP2, MMP9 and VEGF were significantly associated with an increase in tumor size (P<0.05). No significant difference was observed between any of the studied miRNAs regarding lymph node metastasis. Mir-21 was significantly over-expressed in ER-/PR- cases.

CONCLUSION

Specific miRNAs (mir-10, mir-21, mir-155, mir-373, mir-30b, mir-126, mir-17p, mir-335) are associated with tumor metastasis and other clinical characteristics for BC, facilitating identification of individuals who are at risk.

Clinical significance of programmed cell death 4 expression in malignant progression of human nasal inverted papillomas

Programmed cell death 4 (PDCD4) is a novel tumor suppressor gene that can inhibit tumor neoplastic transformation and progression in cultured cells and gene knock-out mouse models. Lost or decreased PDCD4 expression has been associated with progression and prognosis of multiple types of human tumors. However, the expression and clinical significance of PDCD4 in nasal inverted papillomas (NIPs) has not been investigated. We compared PDCD4 expression in 64 samples of NIPs, 23 of associated squamous cell carcinomas (SCCs), and 19 normal nasal samples at mRNA and protein levels by RT-PCR, western blot analysis, and immunohistochemistry. PDCD4 mRNA expression was reduced in 52% of NIP frozen samples (13/25), and the protein level was diminished in 56.3% of samples (36/64) as compared with 19 normal nasal samples, which expressed high levels of PDCD4 mRNA and protein. Furthermore, altered expression of PDCD4 was associated with the clinicopathological features Krouse stage and dysplasia. Importantly, we found a strong negative correlation of PDCD4 expression and Ki-67 labeling index in NIPs (r=-0.6645, p<0.001). In addition, the 3 tissue-sample groups significantly differed in PDCD4 expression and Ki-67 labeling index. Thus, PDCD4 expression may play a key role in pre-cancerous lesions of human NIPs and may help predict malignant progression from benign nasal tumors to associated SCC.

S6 kinase 2 promotes breast cancer cell survival via Akt

The 40S ribosomal protein S6 kinase (S6K) acts downstream of mTOR, which plays important roles in cell proliferation, protein translation, and cell survival and is a target for cancer therapy. mTOR inhibitors are, however, of limited success. Although Akt is believed to act upstream of mTOR, persistent inhibition of p70 S6 kinase or S6K1 can activate Akt via a negative feedback loop. S6K exists as two homologues, S6K1 and S6K2, but little is known about the function of S6K2. In the present study, we have examined the effects of S6K2 on Akt activation and cell survival. Silencing of S6K1 caused a modest decrease, whereas knockdown of S6K2 caused a substantial increase in TNF-α and TRAIL (TNF-related apoptosis-inducing ligand)-mediated apoptosis. In contrast to S6K1, depletion of S6K2 by siRNA decreased basal and TNF-induced Akt phosphorylation. Ectopic expression of constitutively active Akt in MCF-7 cells restored cell survival in S6K2-depleted cells. We have previously shown that activation of Akt induces downregulation of Bid via p53. Knockdown of S6K2 caused an increase in p53, and downregulation of p53 by siRNA decreased Bid level. Silencing of Bid blunted the ability of S6K2 deficiency to enhance TNF-induced apoptosis. Taken together, our study shows that the two homologues of S6K have distinct effects on Akt activation and cell survival. Thus, targeting S6K2 may be an effective therapeutic strategy to treat cancers.